Adenoviruses are promising vectors for therapeutic applications in humans. The striking discrepancy between profound phenotypes of Ad mutants, possessing modifications in individual capsid proteins, and our inability to selectively target tumor cells after intravascular virus delivery underscores poorly appreciated redundancy and overlap of molecular pathways, which become engaged when virus is delivered via intravascular route. This proposal is to conduct comprehensive mechanistic studies to define the contribution of each of the major structural elements of the Ad capsid in mediating virus interaction with liver cells in vivo. Using a large set of previously constructed capsid- modified Ad vectors, we will analyze the role of 1) the fiber structure; 2) the penton-host integrin interactions; and 3) the hexon-blood factor interactions in mediating Ad trapping in the liver and hepatocyte transduction after intravascular Ad delivery. Based on the accumulated data we will 4) construct a lung carcinoma cell-targeted oncolytic Ad vector that escapes trapping by the liver and evaluate its anti-tumor efficacy in a mouse model. These studies will dramatically improve our understanding of the mechanisms governing Ad-host interactions in vivo and will ultimately lead to the development of clinically useful targeted Ad vectors for the therapy of localized and disseminated metastatic tumor diseases.